so whats the deal with Tyr being the head god in northern europe before Odin?
Mmmm, kind of a difficult subject. I will try to keep it as simple as possible, but it is such a broad subject that goes so much farther back in prehistory than "just" the Iron Age, never mind the Viking Age, that it's kind of tough to keep it neat and short.
As you may be aware, the Eddas do not tell us much of Tyr, other than the story of how he lost his hand while fettering Fenris. If you look at oral tradition and some "underlaying currents" - that's if you read between the lines in the sagas and look at the artwork for example - then you get a bit of added information about him. If you look at the symbolism that surrounds Tyr, he comes with all the attributes of a war god, and in later period (read: Viking Age) sagas he is outright said to be
a god of war (notably not
the god of war, probably since the person writing the story was aiming to please someone with ties to Odin).
Many researchers today believe that before the arrival of the Indo-European religions, to which asatru as we know it today belongs, there were goddess worshipping societies all over Europe. It was the Indo-Europeans that then brought the male warrior god worshipping religions to the area. This is more or less undisputed; what's disputed is when, how and why the Indo-Europeans and their religions moved in, and from where. It seems that those goddess worshipping tribes had male gods, too, but in secondary positions relative to The Goddess (Tacitus calls her Nerthus, but it is disputable whether or not this is a misunderstanding or not). For example, the Bronze Age Scandinavian rock carvings depict a set of male twin gods very prominently (actually, those twins are all over the Atlantic seaboard, since it appears us Scandies shared the cult with these people as far down as Malta - we've discussed that before on this board...). Some of the gods that we recognize from the later Viking Age start to appear in the rock carvings
before the arrival of Odin and his companions on the time line axis. Some of the lore also seems to go back to this pre-Odin time. The idea is that Tyr is one of those gods. Jordh could be the remnants of The Goddess. Eliade thinks Thor is one of them, too, but I'm not so sure about that myself.
Some researchers believe that the story that is depicted in the Edda, where the Vanir and Aesir fight a war of soveregnty over the land, is an echo of the actual events that took place when the male warrior IE tribes moved in on the goddess worshipping tribes. Over time a peace was brokered once the populations mixed, just like in the Edda. For this to happen there had to have been two gods of war, one for the goddess' side, and one for the IE side. Some believe that Tyr is the goddess side's god of war, the Vanir, and Odin is the male god's side, the Aesir. Since the gods seem to have survived the clash, neither god of war was erased from the lore.
It could also be something along the lines of Tyr being the original god of war when the IE religion was still new to the area, while Odin was the creator god, the god of wisdom, mead and poetry etc.
Regardless of how it all came about, Odin gradually took over more and more of Tyr's duties. This may have been a result of the political goings on in this world, since different tribes held alegiances to different gods. If those tribes that claimed to be descendants of Odin (or tribes that just supported Odin for whatever reason) were stronger and more successful in battle and/or politics than those who claimed heritage from Tyr, then, naturally, they would hail Odin as their main god of war and it'd be Odin's name that was glorified. It's like Darwins evolution - the survival of the fittest - only here it is the stories of the winners that survive, along with their genes.
- -This is the end of the official answer...hope it made sense! - -
My own personal opinion, if you care, is that Tyr was the main male deity among the goddess worshipping tribes before the arrival of the male god cult. The idea of a Great Earth Goddess mating with a male Sky God to create all the other gods and goddesses, us and the rest of the flora and fauna, is extremely common among societies that are/were at the same stage of development that the Scandy society would have been at when the Goddess cult would have existed (see for example Polynesian religions, the religions on the Russian steppes and the earlier Celtic religion). Tyr has all the markings of a Great Sky God, and he is refered to as such in some of the older oral tradition. Ellis-Davidson (prominent researcher in the field of ON religion) also calls Tyr a sky god, and I think Eliade does, too, but don't quote me on it. Anyhow, at this point, that's speculation on my behalf, but the research article that I am working on right now, with the forge and all that, deals a bit with this, so I am digging around in it a bit and comparing it to other religions, lore, oral tradition and so on. Gimme a year and I'll tell you all about the hieros gamos between the Sky God and the Earth Mother, if I can prove my theory!